Method of making high bulk yarns



United States Patent 3,120,995 METHOD OF MAKIVG IHGH BULK YARNS John Charles Guthrie, Wilmslow, Shirley Norman, Romiley, and Ramon Sidick Mahomed, Kenilworth, England, assignors to Courtaulds Limited, London, England, a British company No Drawing. Filed June 26, 1962, Ser. No. 205,213 Claims priority, application Great Britain June 28, 1961 4 Claims. (Cl. 57157) This invention is concerned with the production of yarns having a high bulk-to-weight ratio.

It has for long been felt desirable to produce viscose rayon yarns having increased bulk, in order to impart improved fullness to viscose rayon-containing fabrics. However, while various methods of bulking yarns of other man-made fibres, especially the wholly synthetic fibres, have been described, none of these methods has proved very successful when applied to viscose rayon fibres.

' An object of this invention is to provide an improved method of producing bulked viscose rayon-containing yarns.

According to the invention, a viscose rayon-containing yarn capable of being bulked is formed by subjecting viscose rayon fibre having a wet extensibility of at least 30 percent to stretching by at least percent and preferably at least percent while wet, drying the stretched fibre while still under tension, and combining the dried fibre with a less shrinkable fibre in a yarn. In the term fibre as used herein we include both staple fibres and continuous filaments.

The invention also includes a bulkable yarn produced by this method and also a viscose yarn or fabric produced by bulking such a yarn.

By the term wet extensibility we mean the increase in length of a wet fibre at its breaking point. Viscose rayon fibres frequently exhibit a wet extensibility below percent, for example of the order of 20 to 25 percent. However, viscose rayon fibres of higher wet extensibility may be prepared by suitably modifying the method employed for producing the fibre. The production of highextensibility fibres suitable for use in this invention will be described later herein in the examples.

The degree of stretch to which the fibre is submitted should be at least 20 percent and is preferably at least 25 percent. However, it is desirable that the stretch applied should not approach unduly closely to the wet extensibility figure, since otherwise the potential shinkage which the stretching operation is designed to introduce may not be fully realised. Moreover, if the fibre is stretched too near to the extensibility limit, there may be insufiicient extensibility of the fibre left after drying for satisfactory subsequent processing of the high-shrinkage fibre, for example its conversion to yarn. It is usually acceptable to submit the fibre to a stretch, expressed as a percentage, up to within 5 or 10 units of the wet extensibility, also expressed as a percentage. For example, a fibre having a wet extensibility of about percent may usually be stretched in the wet state according to this invention by over 30 percent if desired. However, a stretch of 25 to 30 percent will generally be sufiicient to produce satisfactory bulking of the mixed yarn provided that the inherent potential shrinkage of the other component is not unduly high, for example not exceeding 5 percent.

The fibre may be subjected to stretching while immersed in a bath or while still wet from immersion or from spraying with liquid. The bath or liquid is normally aqueous and may be at ambient temperatures or at an elevated temperature. The time of immersion of the fibre in the liquid may vary between wide limits. For example, immersion times of as little as 7 seconds may be used,

3,129,695 Patented Feb. 4, 1 964 or the fibre may remain immersed in or wet with the liquid for several minutes, the tension meanwhile being maintained.

The stretching operation may be applied to the neverdried fibre, i.e. to the fibre before its first drying after spinning, or to the fibre after drying.

The drying of the fibre after stretching may be carried out in batches, for example in an oven, but it is essential that the fibre be kept under tension during drying, with the applied degree of stretch still maintained. A more convenient method is to stretch and dry the fibre continuously in the form of continuous filaments, by first applying the stretch to the wet filaments between pairs of rollers or between single rollers around which the filaments are passed, and subsequently passing the filaments continuously through a heated drying zone. The temperature of the drying zone is dictated largely by practical considerations such as the linear speed of the filaments and does not appear to be critical (within reasonable limits) to the subsequent properties, in particular the potential shrinkage, of the dried fibre.

The fibre may subsequently be combined either as continuous filaments or as staple fibres with the lowershrinkage component of the desired yarn. The preferred arrangement is to mix the high-shrinkage component as staple fibres uniformly or randomly with staple fibres of the other component and to spin a yarn, for example on the cotton, flax or worsted system, from the fibre mixture.

The lower-shrinkage component of the yarn may be another cellulosic fibre, for example a viscose rayon or cellulose acetate fibre; a fibre of a synthetic material, such as polytihylene terephthalate, a polyamide or polyacrylonitrile; a naturally occurring fibre, such as cotton, flax or wool; or a regenerated protein fibre. The difierence in potential shrinkages of the two components depends upon the degree of bulking required. In general a difference of at least 5 or 10 percent potential shrinkage is desirable to obtain a Worthwhile effect, while difierences up to 15 and 20 percent are not diificult to obtain, for example by blending fibres of 15 to 20 percent potential shrinkage with fibres of 0 to 5 percent potential shrinkage, and give admirable bulking.

The relative proportions of the highand low-shrinkage components in the blend forming the yarn may vary between an upper limit (of high-shrinkage fibre), above which there is insufficient low-shrinkage fibre to form the bulk of the bulked yarn, and a lower limit, below which the bulk imparted to the yarn is not very stable. It is preferred to employ between 20 and 50 percent of the high-shrinkage component in the blend. An optimum figure is about 40 percent.

The conversion of the yarn into its higher-bulk form involves an aqueous treatment of the bulkable yarn or of a fabric containing it under relaxed conditions or continuously under conditions allowing shrinkage. The yarn or fabric is immersed in water or an aqueous bath at ambient temperatures or at elevated temperatures near to, or at, the boiling point, for example between and C. Alternatively, the bulking operation may be carried out in steam.

The invention will now be further described by means of the following examples, in which parts and percentages are by weight unless stated otherwise:

Example 1 A viscose containing 7.5 percent of cellulose, 7.0 percent of caustic soda and (based on cellulose), 38 percent of carbon disulphide and 1 percent of a polyethylene glycol modifier (mol. wt. 1500) had a ball-fall viscosity of 50 seconds at 18 C. and a salt figure of 7.0. The viscose was spun through a jet of 40 x 3 mil holes into an aqueous spin bath at 55 C. containing 7.5 percent of sulphuric acid, 7.0 percent of zinc sulphate and 14.5 percent of sodium sulphate, the length of immersion of the spun filaments in the bath being 16 inches.

The filaments were taken up on a godet, stretched by percent to a second godet and thereafter given a further treatment with a hot, 3 percent, aqueous solution of sulphuric acid to complete the regeneration. The filaments were subsequently washed free of acid, desulphurised, bleached and passed through a soft-finish bath. The fibre at this stage had a wet extensibility of 38.8 percent.

The 170-denier tow was now subjected between pairs of rollers to a stretching of 25 percent while immersed in water at 18 C., the path-length of the tow in the water corresponding to an immersion time of 10 seconds. The filaments were passed without reduction in tension through a drying zone at 105 C. and then fed to a cutter where they were converted to staple fibre of 2.5 inch staple length. The staple fibres (measured potential shrinkage in boiling water 18.1 percent) were mixed in a 50/50 mixture with staple fibres of similar length of regenerated viscose which had a nominally zero potential shrinkage, and the staple fibre mixture was spun on the cotton system to a yarn. Samples of the yarn were immersed in boiling water for minutes, during which time the yarn shrank and become more bulky. The increased bulk was maintained when the yarn samples were dried without tension in an oven at 80 C.

Example 2 The viscose employed contained 7 percent of cellulose, 5.8 percent of caustic soda and (all calculated on cellulose) 38 percent of carbon disulphide, 2 percent of a polyethylene glycol (mol. wt. 1500) as a modifier and 0.75 percent of Ethomeen C (an amine/polyethylene glycol modifier). The ball-fall viscosity was 100 seconds at 18 C. and the viscose had a salt figure of 7.1.

This viscose was spun through a 10,000 x 2% mil jet at 1050' gm./minute and with an immersion path of inches into an aqueous spinning bath containing 5.5 percent of sulphuric acid, 7.0 percent of Zinc sulphate, 15 percent of sodium sulphate and 150 parts/million of Ethomeen C25. The bath temperature 'was 55 C.

The spun 3-denier filaments were withdrawn from the bath by a pair of inclined godets rotating at a peripheral speed of 16.7 metres per minute and stretched through a trough containing a hot aqueous stretch liquor on to a second godet pair having a peripheral speed of 30.0 metres per minute (equivalent to an 80 percent stretch). The stretch liquor contained 3.0 percent of sulphuric acid, 0.5 percent of zinc sulphate and 1.0 percent of sodium sulphate. It was at a temperature of 94 C. and the immersion pathlength of the tow in the bath was 5 feet.

The hot, wet tow was thereafter fed on to a continuously moving conveyor, on which it was plaited in a relaxed condition and washed with an aqueous, 1.5 percent solution of sulphuric acid to complete the regeneration. After desulphurisation, washing and finishing, at which stage the filaments had a wet extensibility of 40.5 percent, the tow was stretched by 30 percent between pairs of rollers in water at 18 C. (the immersion time of the tow in the water being about 15 seconds), continuously dried while still under tension in air at 140 C., and fed to a cutter for conversion to 2.5 inch staple fibre. The potential shrinkage of the fibres in boiling water was measured as 17.8 percent. The fibres were blended in a 40/60 mixture with 2.5 inch, 3-denier regenerated cellulose staple fibres having a nominally zero potential shrinkage and spun to an 18s cotton count singles yarn on the cotton system. The

yarn was readily bulked by immersion in boiling water for 10 minutes and subsequently dried relaxed at C. without detriment to its increase in bulk. The degree of bulking was determined by measuring the specific volume of the yarn before and after bulking and an increase of 50 percent was found to have occurred.

Example 3 A tow of viscose rayon filaments was prepared by spinning and hot-stretching as described in Example 2 and, after desulphurisation, washing and finishing as in that example, was stretched by 25 percent between roller pairs in water at 18 C. After drying under tension in air at 140 C., the tow was converted on a Turbostapler tow-to-top converter to a sliver of staple fibres having a staple length of 4 inches.

The sliver was blended with a sliver of similarly prepared viscose rayon staple fibres which had not been coldstretched in water and dried under tension but had been relaxed in steam, to give a yarn containing 40 percent of stretched fibres and 60 percent of the fibres which had not been cold-stretched. The former fibres hada potential shrinkage, of about 18 percent and the latter fibres had a nominally zero potential. shrinkage. The yarn obtained had a cotton count of 24 and was subsequently plied to form a two fold 24s yarn.

The two-fold yarn was next relaxed by immersion in boiling water, the specific volume of the yarn being measured before and after this bulking operation. The efiect of the bulking was to cause an increase in specific volume from 1.43 to 2.30, an increase equivalent to 61 percent.

What we claim is:

1. A method of making a high-bulk yarn, comprising subjecting viscose rayon fibre having a wet extensibility of at least 30 percent to stretching while wet by an amount which is at least 20 percent and is less than the wet extensibility of the fibre by at least 5 units of percentage, drying the stretched fibre while it is under a tension suificient to prevent the fibre from shrinking, forming a yarn consisting of between 20 and 50 percent of the dried fibre and the balance fibre having a potential shrinkage betweenzero and 5 percent, and immersing the yarn in a hot aqueous fluid selected from the group consisting of water at 80 to C. and steam, to cause the stretched fibre to shrink.

2. A method of making a high-bulk yarn, comprising subjecting viscose rayon fibre having a wet extensibility of at least 30 percent to stretching while .wet by an amount which is at least 20 percent and is less than the wet extensibility of the fibre by at least 5 units of percentage, drying the stretched fibre While it is under a tension sufli'cient to prevent the fibre from shrinking, forming a yarn consisting of between 20 and 50 percent of the dried fibre and the balance viscose rayon fibre having a potential shrinkage between zero and 5 percent, and immersing the yarn in a hot aqueous fluid selected from the group consisting of water at 80 to 100 C. and steam, to cause the stretched fibre to shrink.

3. A method according to claim 1, in which the wet fibre when it is subjected to stretching, has never previously been dried.

4. A method according to claim 1, in Which the yarn contains about 40 percent of the stretched fibre.

References Cited in the file of this patent UNITED STATES PATENTS t i 1 l 1 

1. A METHOD OF MAKING A HIGH-BULK YARN, COMPRISING SUBJECTING VISCOSE RAYON FIBRE HAVING A WET EXTENSIBILITY OF AT LEAST 30 PERCENT TO STRETCHING WHILE WET BY AN AMOUNT WHICH IS AT LEAST 20 PERCENT AND IS LESS THAN THE WET EXTENSIBILITY OF THE FIBRE BY AT LEAST 5 UNITS OF PERCENTAGE, DRYING THE STRETCHED FIBRE WHILE IT IS UNDER A TENSION SUFFICIENT TO PREVENT THE FIBRE FROM SHRINKING, FORMING A YARN CONSISTING OF BETWEEN 20 AND 50 PERCENT OF THE DRIED FIBRE AND THE BALANCE FIBRE HAVING A POTENTIAL SHRINKAGE BETWEEN ZERO AND 5 PERCENT, AND IMMERSING THE YARN IN A HOT AQUEOUS FLUID SELECTED FROM THE GROUP CONSISTING OF WATER AT 80* TO 100*C. AND STEAM, TO CAUSE THE STRETCHED FIBRE TO SHRINK. 